An Egyptian court has opened the trial of 16 Americans and 27 other employees of foreign non-profit groups charged with illegal political activities and operating without licenses.

Judge Mahmoud Mohammed Shoukry presided over a chaotic opening session Sunday, before adjourning the trial until April 26. Television reporters crowded around the judge while an Interior Ministry official threatened to expel journalists from the rowdy Cairo chamber.

The defendants have been barred from leaving Egypt. Some others left the country before the travel ban was imposed. Still others have taken refuge at the American Embassy in Cairo.

The 43 pro-democracy activists include Sam LaHood – son of U.S. Transportation Secretary Ray LaHood. They are accused of receiving illegal funds from abroad, carrying out political activities unrelated to their civil society work, and failing to get the necessary operating licenses.

The groups say they have long sought to register in Egypt. The U.S. State Department has said the groups were there to help with elections. It says the Americans are completely unbiased and do not support or raise money for any individual political candidates.

Washington has warned that it could cut $1.3 billion in annual U.S. military aid to Egypt if the trial goes ahead. U.S. officials are holding intense discussions with Egypt to resolve the issue.

Along with 16 Americans and 16 Egyptians, the defendants include Germans, Palestinians, Serbs and Jordanians.

The United States is trying to establish better ties with the military council that took power last year following the ouster of former Egyptian president Hosni Mubarak. U.S. legislators and Egyptian activists say the trial is politically motivated. Rights groups have sharply criticized the investigation, saying it is part of an orchestrated effort by authorities to silence groups critical of the military's handling of the country's democratic transition.

Egyptian officials say the trial has nothing to do with the government and is in the hands of the judiciary.

Also Sunday, Egypt's military rulers called on the newly elected parliament to convene March 3 to elect a 100-member assembly to write the country's first constitution since Mr. Mubarak's overthrow.

A power struggle over the future document is rapidly developing between Egypt's army-backed executive and the Islamist-dominated parliament, which wants to curb broad presidential powers.

Political groups, led by the Muslim Brotherhood's Freedom and Justice Party, already have begun talks on the make-up of the constituent assembly. The panel is expected to include legal experts as well as legislators.